There exist numerous scrambling methods implemented for controlling access to audiovisual information. For example, one solution is provided by the DVB Scrambling method of the digital video broadcasting (DVB) consortium.
Those methods generally make use of an encryption key for scrambling the video signal. The scrambling is generally based on performing an exclusive-OR (XOR) operation between the non-scrambled stream and the encryption key.
For example, in the context of broadcasting programs, a user desiring to access audiovisual information receives the scrambled signal together with a message of the Entitlement Control Message (ECM) type which represents an MPEG-2 Transport Stream (MPEG-2 TS) packet conveying, amongst other things, a decryption key associated with the encryption key. It is the decryption key which is used for unscrambling the video.
Unfortunately, the result of that type of scrambling method is to supply the user with a video signal that is scrambled but that cannot be viewed. The scrambled video signal does not make it possible for the user to get some idea of the audiovisual content prior to unscrambling.